1. Field of the Invention
This invention relates to a method for producing a tin-zinc alloy film, particularly a method for producing a tin-zinc alloy film for corrosion-resistant purposes.
2. Description of the Prior Art
Recently, an attention has been paid to a tin-zinc alloy film to replace for a corrosion-resistant cadmium plating film. Such a cadmium plating film itself has excellent corrosion-resistance and thus, is employed as a material for an aircraft at present. However, the cadmium plating film is strictly restricted in use because it has harmful element, Cd for environment. In this point of view, the use of the cadmium plating film would be more severely restricted in future. Therefore, the tin-zinc alloy film would play very important roles in future instead of the cadmium plating film.
In the past, the tin-zinc film would be produced from a given water solution by means of alloy-electroplating, and thus, two different metals, tin and zinc, must be electroplated at the same voltage. Therefore, all kinds of things to perform the electroplating at the same voltage have been carried out. Moreover, chemical species to be used have been restricted, and anti-environmental additives have been used.
Furthermore, the above electroplated tin-zinc film from the water solution always has a thermally non-equilibrium phase which is not recognized in its equilibrium diagram. The non-equilibrium phase often shifts to another stable phase due to the wear or the heating in the use of the tin-zinc alloy film, and thus, the properties of the tin-zinc alloy film often change. Therefore, the functions imparted to the tin-zinc alloy film for predetermined purposes may change during the use of the film, so that it may be that the tin-zinc alloy film can not exhibit the predetermined functions in use.
Such a technique is described in Japanese Patent Application Laid-open No. 01-165791 as plating a zinc film and a tin film in their respective predetermined thickness on a given steel plate and then, melting the tin film and diffusing the tin elements into the zinc film through a given thermal treatment, to produce a tin-zinc alloy film. With such a technique, however, the tin elements and the zinc elements are inclined in the tin-zinc alloy film in concentration, so that the tin elements and the zinc elements can not be alloyed perfectly.
It is an object of the present invention to provide a method for producing a stable tin-zinc alloy where the tin elements and the zinc elements are perfectly alloyed and the predetermined functions such as corrosion-resistance can be exhibited sufficiently.
For achieving the above object, this invention relates to a method for producing a tin-zinc alloy film comprising the steps of:
depositing a tin layer and a zinc layer on a given substrate sequentially, thereby to form a multilayered film composed of the tin layer and the zinc layer, and
irradiating a laser beam onto the multilayered film to produce a tin-zinc alloy film.
The inventors had intensely studied to alloy tin elements and zinc elements perfectly, to obtain a uniform and stable tin-zinc alloy film. As a result, they found out that a tin layer and a zinc layer which includes the tin elements and the zinc elements are stack, and then, a given laser beam is irradiated onto the thus obtained multilayered film, to alloy the tin elements and the zinc elements perfectly through the inter-diffusion and produce a tin-zinc alloy film desired which can exhibit excellent corrosion-resistance in use for a long time.
According to the present invention, the tin-zinc alloy film, where the tin elements and the zinc elements are perfectly and uniformly alloyed, can be is produced through the inter-diffusion between the tin elements and the zinc elements in a short time without the creation of a non-equilibrium phase. Therefore, various functions such as corrosion-resistance imparted to the tin-zinc alloy film in advance can be maintained for a long time, and thus, the running cost for the tin-zinc alloy film can be reduced because the producing period of time for the alloy film can be shortened.